Generating mobile device-specific identifiers across native mobile applications and mobile browsers

ABSTRACT

Described herein are methods and systems for generating a mobile device-specific identifier usable across native mobile applications and mobile browsers with a unified opt-out mechanism. A mobile device generates a transient identifier for the mobile device and maps the transient identifier to a stable identifier of the mobile device using at least one call to a service endpoint coupled to the mobile device via a communications network. A browser application on the mobile device renders a webpage, the webpage comprising first instructions, executed by the browser application, to retrieve the stable identifier of the mobile device using at least one call to the service endpoint coupled to the mobile device via a communications network.

TECHNICAL FIELD

The subject matter of this application relates generally to methods andapparatuses, including computer program products, for generating amobile device-specific identifier usable across native mobileapplications and mobile browsers—including using the mobiledevice-specific identifier for a unified retargeting opt-out mechanism.

BACKGROUND

Generally, mobile device targeting and retargeting for ad purposesutilizes two different methodologies in order to identify a mobiledevice and provide device-specific ads: one for native applicationsinstalled on the mobile device and another for websites rendered by abrowser application on the mobile device. For native applications, asoftware module (such as an SDK) embedded in the native application cancapture a device-specific identifier (e.g., IDFA in Apple iOS™, AAID forAndroid™) when sharing of the device-specific identifier is enabled bythe user. In order to opt-out of retargeting activity, a user can simplyturn off sharing of the device-specific identifier in the settings ofthe mobile device, and the device is no longer retargetable.

For mobile browsers, websites can drop cookies (e.g., first-partycookies, third-party cookies) to track the user's activity in thebrowser for retargeting purposes. Recent developments—such as Apple'sintegration of Intelligent Tracking Prevention (ITP) in the most recentversion of its Safari™ mobile browser—are trying to limit retargeting inmobile browsers by blocking or partitioning cookies for domains flaggedas “trackers.” As a result, when serving browser-based ads, suchtracking domains are unable to identify the user or mobile device andits activity history in order to deliver a user- or device-specific ad.

However, these developments also create an asymmetry between the wayusers can opt-out of tracking for mobile applications and in the mobilebrowser. As noted above, for native applications, users can switch offtheir device-specific identifier which will stop targeting in all nativeapplications. No such mechanism exists for the mobile browser. As such,initiatives such as ITP may make it more difficult to implement areliable in-browser opt-out mechanism for mobile devices.

SUMMARY

Therefore, what is needed are methods and systems to automatically tiethe in-browser identity of the mobile device with the device-specificidentifier used by native applications, in order to advantageouslycreate a unified retargeting opt-out mechanism that only relies ondisabling the device-specific identifier. The techniques describedherein overcome several limitations with current retargeting technology,including providing the ability for seamless integration of browseridentity with the device-specific identifier, without requiring theability to drop third-party cookies on certain domains in the browser.In addition, the methods and systems herein improve existing technicaloperation of the mobile device through the generation of a transientidentifier (TID) for the device which is then associated with thedevice-specific identifier; this allows the browser to retrieve thedevice-specific identifier and persist it as a locally-stored value (byusing, for instance, first-party cookies, or local storage) to bothenable integrated retargeting across both native apps and the mobilebrowser and to provide the unified opt-out mechanism described above.

Generally, the technical solution presented herein is based on atwo-step approach:

-   -   A transient identifier (TID) is generated for the mobile device        that is not based on cookies, but on device fingerprinting. The        lifespan of a TID may be short, i.e. TIDs may change when the        device wakes up from sleep or switches to a different network        interface, such as switching between WiFi and cellular        connectivity.    -   The TIDs are mapped to the device-specific identifier (“Device        ID”), such as IDFA on iPhone™ or AAID on Android™-based devices,        using one or a combination of: SDK support in native        applications on the mobile device; by buying ad displays in the        native application; or using a tracking pixel that is called        from the native application. Once the TID is mapped to a Device        ID, the information can be retrieved in the browser by calling a        service endpoint that will retrieve the Device ID based on the        TID, and persist it by dropping locally-stored values (such as a        first-party cookie, or local storage) on as many domains as        possible that are visited by the mobile device in the browser        application while the TID remains stable. This activity        associates the mobile browser with the Device ID on those        visited domains in a persistent manner, for the lifetime of the        locally-stored values.

The system can then implement an opt-out mechanism based on the DeviceID. For example, the system monitors the appearance of a particularDevice ID on real-time bidding platforms (RTBs) for in-app ad inventory,as well as on in-app ad inventory that is managed directly via an SDK.Before showing an ad in the mobile browser, the system can check whetherthe Device ID has been seen recently, e.g. during the last twenty-fouror forty-eight hours. The system then suppresses the ad if the Device IDhas not been seen recently. This provides a reliable “eventual opt-out”mechanism for the mobile browser. Also, in order to protect the privacyof users and to limit tracking by third-parties, the locally-storedvalues dropped by the system contain a salted and encrypted version ofthe Device ID; these locally-stored values are eventually deleted fordevices that have stopped sharing their Device ID and are thusconsidered to have been opted out.

The invention, in one aspect, features a system for generating a mobiledevice-specific identifier usable across native mobile applications andmobile browsers. The system includes a mobile device that calls aservice endpoint coupled to the mobile device via a communicationsnetwork and passes a stable identifier as a parameter to the serviceendpoint. The service endpoint generates a transient identifier for themobile device and maps the transient identifier to the stable identifierof the mobile device. The mobile device renders a webpage in a browserapplication, the webpage comprising first instructions, executed by thebrowser application, to retrieve the stable identifier of the mobiledevice using at least one call to the service endpoint coupled to themobile device via the communications network. The mobile device storesthe stable identifier of the mobile device in the browser application asa locally-stored value.

The invention, in another aspect, features a computerized method ofgenerating a mobile device-specific identifier usable across nativemobile applications and mobile browsers. A mobile device calls a serviceendpoint coupled to the mobile device via a communications network, andpasses a stable identifier as a parameter to the service endpoint. Theservice endpoint generates a transient identifier for the mobile deviceand maps the transient identifier to the stable identifier. The mobiledevice renders a webpage in a browser application, the webpagecomprising first instructions, executed by the browser application, toretrieve the stable identifier of the mobile device using at least onecall to the service endpoint coupled to the mobile device via acommunications network, and to store the stable identifier of the mobiledevice as a locally-stored value.

Any of the above aspects can include one or more of the followingfeatures. In some embodiments, the stable identifier is an iOS™ IDFA. Insome embodiments, the stable identifier is an Android™ AAID. In someembodiments, the retrieved stable identifier is based at least in parton the locally-stored value in the browser application.

In some embodiments, the webpage contains second instructions to trackuser activity based on the retrieved stable identifier. In someembodiments, tracking user activity comprises capturing one or moreattributes associated with user activity on a website in the browserapplication. In some embodiments, user activity comprises one or moreof: a visit to a product webpage, a search for a product, a visit to acategory webpage, an add-to-cart action, or a completion of atransaction. In some embodiments, the website is an ecommerce retailerwebsite.

In some embodiments, the webpage contains third instructions to identifythe mobile device to an ad server or an RTB platform based on theretrieved stable identifier, as part of a bid request associated with atleast one ad impression opportunity.

In some embodiments, generating a transient identifier for the mobiledevice and mapping the transient identifier to the stable identifier ofthe mobile device using at least one call to a service endpointcomprises: retrieving, by the mobile device, the stable identifier ofthe mobile device; establishing, by the mobile device, a connection tothe service endpoint; sending, by the mobile device, the stableidentifier to the service endpoint; generating, by the service endpoint,the transient identifier; and storing, by the service endpoint, amapping between the transient identifier and the stable identifier ofthe mobile device.

In some embodiments, establishing a connection to the service endpointcomprises: establishing, by the mobile device, a TCP connection to theservice endpoint; and sending, by the mobile device, an HTTP request(e.g., HTTP GET) over the TCP connection; in an alternate embodiment,other types of HTTP requests (e.g., HTTP POST) may be used. In someembodiments, establishing a connection to the service endpoint comprisesestablishing, by the mobile device, a TCP connection to the serviceendpoint, and sending, by the mobile device, an HTTPS request (e.g.,HTTPS GET) over the TCP connection; in an alternate embodiment, othertypes of HTTPS requests (e.g., HTTPS POST) may be used. In someembodiments, generating the transient identifier by the service endpointcomprises: extracting at least one of TSval or TSecr from TCP timestampoptions of at least one TCP packet received from the mobile device overthe TCP connection; and generating the transient identifier using atleast one of TSval, TSecr, a clock time associated with the serviceendpoint, and a source IP address of the TCP connection. In someembodiments, the service endpoint determines a latency associated withthe TCP connection using TSecr and the clock time of the serviceendpoint, and generates the transient identifier using a concatenationof (i) the source IP address and (ii) a difference between the clocktime of the service endpoint, TSval, and the latency associated with theTCP connection.

In some embodiments, generating the transient identifier by the serviceendpoint comprises identifying the source IPv6 address of the TCPconnection, and generating the transient identifier using the sourceIPv6 address. In some embodiments, the service endpoint identifies thesource IP address of the TCP connection, determines that the identifiedsource IP address is included in a blacklist, and discards one or morerequests for a transient identifier that are associated with theidentified source IP address. In one embodiment, the blacklist containsIP addresses that generate substantial amounts of traffic with the sametransient identifiers. In some embodiments, the IP addresses correspondto proxies or to fraudulent traffic.

In some embodiments, the service endpoint allocates the transientidentifier to one of a plurality of buckets to generate an updatedtransient identifier. In some embodiments, the mobile device combinesthe transient identifier received from the service endpoint with one ormore data elements associated with the mobile device. In someembodiments, allocation to one of a plurality of buckets is achieved bydividing a value range of the transient identifier into a number ofequally-sized intervals, and computing a floor of the transientidentifier divided by the size of an interval. In some embodiments, thenumber of buckets is 4096.

In some embodiments, retrieving the stable identifier of the mobiledevice using at least one call to the service endpoint comprises:establishing, by the mobile device, a connection to the serviceendpoint; generating, by the service endpoint, a first transientidentifier; retrieving, by the service endpoint, the stable identifierof the mobile device, using a mapping between the first transientidentifier and the stable identifier of the mobile device; and sending,by the service endpoint to the mobile device, the stable identifier ofthe mobile device.

In some embodiments, generating a transient identifier for the mobiledevice and mapping the transient identifier to the stable identifier ofthe mobile device using at least one call to a service endpointcomprises: establishing, by the mobile device, a plurality ofconnections to a second service endpoint, each connection on a differentsubdomain, wherein when establishing the plurality of connections, themobile device performs Domain Name System (DNS) resolution on eachdifferent subdomain to generate an IP address for the subdomain;generating, for each DNS resolution, by a DNS server associated to eachdifferent subdomain, an IP address for the associated subdomaincomprising a random subset of bits; extracting and returning, by thesecond service endpoint, the random subset of bits for each of theplurality of connections; generating, by the mobile device, thetransient identifier using at least one of the returned random subsetsof bits from each DNS resolution; retrieving, by the mobile device, thestable identifier of the mobile device; establishing, by the mobiledevice, a connection to the service endpoint; sending, by the mobiledevice, the stable identifier of the mobile device and the transientidentifier to the service endpoint; and storing, by the serviceendpoint, a mapping between the transient identifier and the stableidentifier of the mobile device.

In some embodiments, generating the transient identifier using each ofthe random subsets of bits from each DNS resolution comprises:identifying, by the second service endpoint for each connection, the IPaddress on which the second service endpoint is called; extracting, bythe second service endpoint for each connection, the random subset ofbits from the IP address; transmitting, by the second service endpointfor each connection, the random subset of bits to the mobile device; andconcatenating, by the mobile device, each of the random subsets of bitsreceived from the second service endpoint to generate the transientidentifier.

In some embodiments, the first service endpoint and the second serviceendpoint are the same. In some embodiments, the plurality of connectionsto the second service endpoint is initiated by the mobile device. Insome embodiments, a first of the plurality of connections to the secondservice endpoint is initiated by the mobile device and the rest of theplurality of connections to the second service endpoint is controlled bythe second service endpoint via redirects.

In some embodiments, generating the transient identifier using each ofthe random subsets of bits from each DNS resolution comprises:identifying, by the second service endpoint for a first connection ofthe plurality of connections, the IP address on which the second serviceendpoint is called; extracting, by the second service endpoint for thefirst connection, the random subset of bits from the IP address;extracting, by the second service endpoint for each connection, therandom subset of bits from the IP address; transmitting, by the secondservice endpoint for each connection, the random subset of bits to themobile device; and concatenating, by the mobile device, each of therandom subsets of bits received from the second service endpoint togenerate the transient identifier. In some embodiments, generating atransient identifier for the mobile device and mapping the transientidentifier to the stable identifier of the mobile device using at leastone call to a service endpoint comprises: establishing, by the mobiledevice, a plurality of connections to a second service endpoint, eachconnection on a different subdomain, wherein when establishing theplurality of connections, the mobile device performs Domain Name System(DNS) resolution on each different subdomain to generate an IP addressfor the subdomain; generating, for each DNS resolution, by a DNS serverassociated to each different subdomain, an IP address for the associatedsubdomain comprising a random subset of bits; extracting, by the secondservice endpoint for the first connection, the random subset of bitsfrom the IP address; redirecting, by the second service endpoint, toeach of the other plurality of connections on a different subdomainsequentially, wherein on each redirection the second service endpointpasses the extracted random subsets of bits to the redirectedconnection, extracts the random subset of bits from the IP address ofthe redirected connection, and concatenates the extracted random subsetof bits to the passed extracted random subsets of bits to form aconcatenated value that forms a new extracted random subset of bits;using, by the second service endpoint, upon a last redirection, theconcatenated value as the generated transient identifier; retrieving, bythe mobile device, the stable identifier of the mobile device;establishing, by the mobile device, a connection to the serviceendpoint; sending, by the mobile device, the stable identifier of themobile device and the transient identifier to the service endpoint; andstoring, by the second service endpoint, a mapping between the transientidentifier and the stable identifier of the mobile device

In some embodiments, the second service endpoint identifies the sourceIP address of each of the plurality of connections, determines that oneor more of the identified source IP addresses is included in ablacklist, and discards one or more requests that are associated withthe identified source IP addresses. In some embodiments, the mobiledevice stores DNS resolution data comprising a mapping of each subdomainto its corresponding IP address in a DNS cache of the mobile device. Insome embodiments, the DNS server associated to each different subdomainsets a time-to-live (TTL) of the DNS resolution data to a predeterminedvalue. In some embodiments, the predetermined value is at least one day.

In some embodiments, the random subset of bits from the IP address forthe associated subdomain is at least 8 bits, corresponding to a class Crange of IP addresses. In some embodiments, the random subset of bitsfrom the IP address for the associated subdomain is at least 16 bits,corresponding to a class B range of IP addresses.

In some embodiments, the mobile device generates a device-specificidentifier for the mobile device; appends the device-specific identifierto each different subdomain to generate device-specific subdomains thatare one level deeper than each different subdomain; performs the DNSresolution using the device-specific subdomains; and the DNS serverassociated to each different subdomain generates, for each DNSresolution using the device-specific subdomain, an IP address for thedevice-specific subdomain comprising a random subset of bits. In someembodiments, at least one connection between the mobile device and thesecond service endpoint on a device-specific subdomain is an HTTPSconnection. In some embodiments, the mobile device generates adevice-specific identifier for the mobile device; performs the DNSresolution using each of the different subdomains; uses the secondendpoint to generate a first transient identifier; and appends thedevice-specific identifier to the first transient identifier to obtain asecond transient identifier. In some embodiments, the device-specificidentifier for the mobile device is generated based on an IP address ofthe mobile device. In some embodiments, the device-specific identifierfor the mobile device is a hash of an IP address of the mobile device.In some embodiments, the mobile device obtains the IP address of themobile device by calling a service endpoint that returns a source IPaddress. In some embodiments, the mobile device combines the transientidentifier received from the service endpoint with another transientidentifier generated by the mobile device to form an updated transientidentifier. In some embodiments, the mobile device combines thegenerated transient identifier with one or more data elements associatedwith the mobile device to form an updated transient identifier. In someembodiments, the one or more data elements associated with the mobiledevice comprise at least one of: a device model, a language setting, ora software version.

In some embodiments, the mapping comprises the transient identifier, thestable identifier, a mapping expiration time, and an identifier of amethod used to generate the transient identifier.

In some embodiments, retrieving the stable identifier of the mobiledevice, using at least one call to the service endpoint comprises:retrieving, by the service endpoint, the transient identifier;determining, by the service endpoint, whether a non-expired mappingexists between the transient identifier and the stable identifier;transmitting, by the service endpoint, the stable identifier to themobile device if a non-expired mapping exists; and transmitting, by theservice endpoint, a null value to the mobile device if no mapping existsor if an expired mapping exists.

In some embodiments, generating a transient identifier for the mobiledevice and mapping the transient identifier to a stable identifier ofthe mobile device is initiated by an SDK within a native applicationinstalled on the mobile device. In some embodiments, generating atransient identifier for the mobile device and mapping the transientidentifier to a stable identifier of the mobile device is initiated uponan occurrence of one or more events detected by the SDK at the mobiledevice. In some embodiments, the one or more events comprise a reboot ofthe mobile device, a waking from sleep of the mobile device, a networkinterface change of the mobile device, a connectivity change of themobile device, or an elapsing of a predetermined time interval.

In some embodiments, generating a transient identifier for the mobiledevice and mapping the transient identifier to a stable identifier ofthe mobile device is initiated by code associated with an ad impressionrendered in a native application installed on the mobile device. In someembodiments, the stable identifier is embedded within the codeassociated with the ad impression and the mobile device extracts thestable identifier for transmission to the service endpoint as part ofthe call to the service endpoint. In some embodiments, the stableidentifier is included in an URL stored in the code associated with thead impression. In some embodiments, a bid is submitted for the adimpression by an ad server based upon prior activity associated with thestable identifier of the mobile device. In some embodiments, a bid issubmitted for the ad impression by an ad server upon receiving a bidrequest for an ad impression in a native application installed on themobile device, where the bid request identifies the mobile device viaits stable identifier, and the ad server determines that a mappingbetween the transient identifier and the stable identifier does notexist. In some embodiments, a bid is submitted for the ad impression byan ad server upon receiving a bid request for an ad impression in anative application installed on the mobile device, where the bid requestidentifies the mobile device via its stable identifier, and the adserver determines that a mapping between the transient identifier andthe stable identifier has expired. In some embodiments, a bid issubmitted for the ad impression by an ad server upon receiving a bidrequest for an ad impression in a native application installed on themobile device, where the bid request identifies the mobile device viaits stable identifier, and the ad server determines that a mappingbetween the transient identifier and the stable identifier has beeninvalidated by a change in network connectivity for the mobile device.

In some embodiments, generating a transient identifier for the mobiledevice and mapping the transient identifier to a stable identifier ofthe mobile device is initiated by a pixel called from a nativeapplication installed on the mobile device.

In some embodiments, executing the first instructions to retrieve thestable identifier of the mobile device comprises: identifying, by thebrowser application executing the first instructions, a locally-storedvalue that includes a first stable identifier on the domain of thewebpage and extracting the first stable identifier from thelocally-stored value; calling, by the browser application executing thefirst instructions, the service endpoint, and passing the first stableidentifier as an argument; generating, by the service endpoint, atransient identifier; determining, by the service endpoint, a secondstable identifier of the mobile device using one or more of thetransient identifier, the first stable identifier, and a mapping betweenthe transient identifier and a third stable identifier; receiving, bythe browser application executing the first instructions, the secondstable identifier from the service endpoint; and storing, by the browserapplication executing the first instructions, the second stableidentifier in a locally-stored value. In some embodiments, the serviceendpoint updates a mapping between the transient identifier and thethird stable identifier using the received first stable identifier. Insome embodiments, the locally-stored value is in one or more of: afirst-party cookie, a third-party cookie, a partitioned third-partycookie, a browser cache, a partitioned browser cache, or a localstorage.

In some embodiments, when a locally-stored value that includes the firststable identifier is not identified, the browser application, executingthe first instructions, sets the first stable identifier to a nullvalue. In some embodiments, when the second stable identifier receivedfrom the service endpoint is a null value, the browser application,executing the first instructions, clears the locally-stored value thatincludes the first stable identifier. In some embodiments, when thesecond stable identifier received from the service endpoint is anon-null value and the locally-stored value that includes the firststable identifier is not identified, the browser application, executingthe first instructions, sets the locally-stored value that includes thesecond stable identifier. In some embodiments, when the second stableidentifier received from the service endpoint is a non-null value thatis different from the first stable identifier, the browser applicationupdates the locally-stored value to include the second stable identifierdetermined by the service endpoint.

In some embodiments, the stable identifier included in thelocally-stored value is an encrypted value derived from the stableidentifier. In some embodiments, the service endpoint generates theencrypted value using the second stable identifier, a timestamp, arandom salt value, and a secret symmetric encryption key.

In some embodiments, executing the third instructions to identify themobile device to an ad server or an RTB platform comprises: determining,by the browser application, a locally-stored value that includes thestable identifier; extracting, by the browser application, the stableidentifier from the locally-stored value; and passing, by the browserapplication, the stable identifier to the ad server or the RTB platform.In some embodiments, generating a transient identifier for the mobiledevice and mapping the transient identifier to a stable identifier ofthe mobile device using at least one call to a service endpoint coupledto the mobile device comprises determining, by the mobile device,whether sharing of the stable identifier of the mobile device isdisabled in the mobile device, and sending, by the mobile device, a nullvalue for the stable identifier of the mobile device when sharing of thestable identifier is disabled in the mobile device.

In some embodiments, retrieving the stable identifier of the mobiledevice using at least one call to the service endpoint comprisesdetermining whether the service endpoint has a non-expired secondmapping between the stable identifier of the mobile device and atimestamp. In some embodiments, the second mapping between the stableidentifier of the mobile device and the timestamp expires after a giventime. In some embodiments, when the service endpoint does not have anon-expired second mapping between the stable identifier of the mobiledevice and the timestamp, the service endpoint returns a null value forthe stable identifier of the mobile device to the browser application.In some embodiments, the browser application passes a null value for thestable identifier of the mobile device to the ad server or the RTBplatform. In some embodiments, the second mapping between the stableidentifier of the mobile device and the timestamp expires after 24hours, 48 hours, or 72 hours.

In some embodiments, a native application on the mobile device generatesone or more bid requests associated with one or more ad impressions inthe native application, the one or more bid requests including thestable identifier of the mobile device, where the one or more bidrequests are processed by an ad server or an RTB platform and sent to atleast one second remote computing device, where the at least one secondremote computing device extracts the stable identifier from the one ormore bid requests, and where the at least one second remote computingdevice updates the second mapping between the stable identifier of themobile device and the timestamp with the current time. In someembodiments, updating the second mapping between the stable identifierof the mobile device and the timestamp comprises creating the secondmapping between the stable identifier of the mobile device and thetimestamp if the second mapping does not exist, or changing thetimestamp to the current time if the second mapping exists.

The invention, in another aspect, features a system for opting out of adretargeting in a browser application of a mobile device. The systemincludes a browser application of a mobile device that renders awebpage. The webpage includes first instructions, executed by thebrowser application, to retrieve a stable identifier of the mobiledevice, determine, based upon the retrieved stable identifier, whethersharing of the device identifier is disabled in the mobile device, andidentify the mobile device to an ad server or an RTB platform based onthe retrieved stable identifier, as part of a bid request associatedwith at least one ad impression, when sharing of the device identifieris not disabled in the mobile device.

The above aspect can include one or more of the following features. Insome embodiments, the stable identifier and the device identifier arethe same. In some embodiments, the stable identifier is an Apple™ IDFA.In some embodiments, the stable identifier is an Android™ AAID. In someembodiments, retrieving a stable identifier of the mobile devicecomprises retrieving the stable identifier from a locally-stored value.In some embodiments, the locally-stored value comprises a first-partycookie, a third-party cookie, a browser cache, or local storage. In someembodiments, when sharing of the device identifier is disabled in themobile device, retrieving a stable identifier of a mobile device returnsa null value for the stable identifier of the mobile device. In someembodiments, when sharing of the device identifier is disabled in themobile device, the mobile device clears the locally-stored value thatincludes the stable identifier of the mobile device.

In some embodiments, retrieving a stable identifier of the mobile devicecomprises retrieving the stable identifier using at least one call to aservice endpoint coupled to the mobile device via a communicationsnetwork. In some embodiments, retrieving a stable identifier of themobile device using at least one call to a service endpoint comprises:generating, by the service endpoint, a transient identifier for themobile device; determining, by the service endpoint, the stableidentifier of the mobile device by using a mapping between the transientidentifier and the stable identifier of the mobile device; determining,by the service endpoint, whether sharing of the device identifier isdisabled in the mobile device by using a second mapping; and if sharingof the device identifier in the mobile device is disabled, returning anull value for the stable identifier from the at least one call to aservice endpoint.

In some embodiments, determining whether sharing of the deviceidentifier is disabled in the mobile device comprises calling a serviceendpoint to check a second mapping between the device identifier and atimestamp. In some embodiments, sharing of the device identifier isdetermined to be disabled in the mobile device when the timestamp, inthe second mapping between the stable identifier and a timestamp, isolder than a defined time period. In some embodiments, the defined timeperiod is 24 hours, 48 hours, or 72 hours.

In some embodiments, a native application on the mobile device generatesone or more bid requests associated with one or more ad impressions inthe native application, the one or more bid requests including thestable identifier of the mobile device; wherein the one or more bidrequests are processed by an ad server or an RTB platform and sent to atleast one second remote computing device; wherein the at least onesecond remote computing device extracts the stable identifier from theone or more bid requests; and where the at least one second remotecomputing device updates the second mapping between the stableidentifier of the mobile device and the timestamp with the current time.In some embodiments, a pixel called from a native application installedon the mobile device generates a request to a service endpointimplemented by at least one second remote computing device, the requestcomprising the stable identifier of the mobile device; wherein the atleast one second remote computing device extracts the stable identifierfrom the request; and wherein the at least one second remote computingdevice updates the second mapping between the stable identifier of themobile device and the timestamp with the current time. In someembodiments, an SDK within a native application on the mobile devicegenerates one or more bid requests associated with one or more adimpressions in the native application, the one or more bid requestsincluding the stable identifier of the mobile device; wherein the one ormore bid requests are processed by an ad server or an RTB platform andsent to at least one second remote computing device; where the at leastone second remote computing device extracts the stable identifier fromthe one or more bid request; and where the at least one second remotecomputing device updates the second mapping between the stableidentifier of the mobile device and the timestamp with the current time.

In some embodiments, when sharing of the device identifier is disabledin the mobile device, the mobile device clears locally-stored valuesthat include the stable identifier of the mobile device. In someembodiments, the locally-stored values are in one or more of: afirst-party cookie, a third-party cookie, a partitioned third-partycookie, a browser cache, a partitioned browser cache, or a localstorage.

Other aspects and advantages of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, illustrating the principles of the invention byway of example only.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the invention described above, together with furtheradvantages, may be better understood by referring to the followingdescription taken in conjunction with the accompanying drawings. Thedrawings are not necessarily to scale, emphasis instead generally beingplaced upon illustrating the principles of the invention.

FIG. 1 is a block diagram of a system for generating a mobiledevice-specific identifier usable across native mobile applications andmobile browsers.

FIG. 2 is a flow diagram of a method of generating a mobiledevice-specific identifier usable across native mobile applications andmobile browsers.

FIG. 3 is a ladder diagram of a method of generating a TID based upon aDNS Caching technique.

FIG. 4 is a ladder diagram of a method of generating a TID based upon aTCP timestamp technique.

FIG. 5 is a flow diagram of a method of mapping the TID and the DeviceIDvia a native application on the mobile device.

FIG. 6 is a flow diagram of a method of mapping the TID and the DeviceIDvia in-app advertisements on the mobile device.

FIG. 7 is a flow diagram of a method of buying an ad impression based onwhether a non-expired mapping exists in the mapping table for a givenDeviceID.

FIG. 8 is a flow diagram of a method of obtaining the stable identifierfor the mobile device for use in a mobile browser application.

FIG. 9 is a flow diagram of a method of using the stable identifier tobid for ad impressions in a mobile browser application.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a system 100 for generating a mobiledevice-specific identifier usable across native mobile applications andmobile browsers. As illustrated, networked system 100 includes a mobileclient computing device 102 that is capable of executing a nativeapplication 103 a and a browser application 103 b. Exemplary mobiledevices 102 include, but are not limited to, tablets, smartphones, andsmart watches. It should be appreciated that other types of computingdevices that are capable of connecting to the components of the system100 can be used without departing from the scope of invention. AlthoughFIG. 1 depicts a single mobile computing device 102, it should beappreciated that the system 100 can include any number of mobiledevices.

The native application 103 a is a software application (also called an‘app’) that is installed locally on the mobile device 102 and writtenwith programmatic code designed to interact with an operating systemthat is native to the mobile device 102. Such software is availablefrom, e.g., the Apple® App Store or the Google® Play Store. In someembodiments, the native application 103 a includes a softwaredevelopment kit (SDK) module that is executed by a processor of themobile device 102 to perform functions associated with generating amobile device-specific identifier usable across native mobileapplications and mobile browsers as described herein.

The browser application 103 b comprises software executing on aprocessor of the mobile device 102 that enables the mobile device tocommunicate via HTTP or HTTPS with remote servers addressable with URLs(e.g., web server 108) to receive website-related content, including oneor more webpages, for rendering in the browser application andpresentation on a display device coupled to the mobile device 102.Exemplary mobile browser application software includes, but is notlimited to, Firefox™, Chrome™, Safari™, and other similar software. Theone or more webpages can comprise visual and audio content for displayto and interaction with a user. In some embodiments, the one or morewebpages can include code for the rendering of ad impressions.

The system 100 also includes a service endpoint 106 which is acombination of hardware, including one or more special-purposeprocessors and one or more physical memory modules, and specializedsoftware engines that execute on the processor of the service endpoint106, to receive data from other components of the system 100, transmitdata to other components of the system 100, and perform functionsrelating to generating a mobile device-specific identifier usable acrossnative mobile applications and mobile browsers as described herein. Insome embodiments, the service endpoint 106 executes specialized sets ofcomputer software instructions programmed onto a dedicated processor inthe service endpoint 106 and can include specifically-designated memorylocations and/or registers for executing the specialized computersoftware instructions. It should be appreciated that, although FIG. 1depicts a single service endpoint 106, the system 100 can include aplurality of service endpoints to provide the functionality describedherein.

The system 100 also includes a web server 108 (e.g., a computing deviceor devices) that hosts a website, to which the mobile device 102connects to retrieve and display webpage content. In some embodiments,the website is an e-commerce platform from a retailer selling onlinegoods or services. In some embodiments, the website is an online contentplatform (e.g., owned and maintained by a publisher) that sells adimpressions or other types of advertising placements (e.g., for adcreatives, audio/video ads, and other content). Typically, the websitecomprises a plurality of visual and non-visual elements that make up thecontent transmitted and displayed to a user when, e.g., browser software103 b on the mobile device 102 connects to the web server 106 via acommunications network 104 (e.g., Internet) and requests content fromthe website. The elements of a website include, but are not limited to,webpages (e.g., HTML documents), image files, layouts, color sets,stylesheets, document object models (DOM), tracking elements,instrumentations (e.g., analytics, advertisement display, etc.),metadata, URLs, advertisements, and content (e.g., text, audio, video).

The system 100 also includes an ad system 110 and a real-time bidding(RTB) platform 112, each of which can comprise a server computing deviceor multiple server computing devices. In some embodiments, ad system 110can collect behavioral data for a plurality of devices, browsers, and/orapplications. In some embodiments, the ad system 110 can receivebehavioral data for a plurality of devices, browsers, and/orapplications from third-parties. In some embodiments, the ad system 110can provide graphical display source code for a computerized graphicaladvertisement display in accordance with the present technology. In someembodiments, ad system 110 is a DSP (Demand-Side Platform) or aretargeting platform.

The RTB platform 112 can perform auctions for advertising displayopportunities in online media, such as application content in the nativeapplication 103 a, or webpages served by web server 108, that areprovided to the browser application 103 b. For example, ad system 110can receive bid requests for such advertising opportunities from RTBplatform 112 and submit bids to RTB platform 112; if the RTB platform112 determines that ad system 110 wins the auction, ad system 110 canprovide source code or other display data for a computerized graphicaladvertisement display to fill the advertising display opportunity in awebpage rendered by the browser application 103 b or by the nativeapplication 103 a on the mobile device 102.

The network 104 enables the various devices 102, 106, 108, 110, 112, 114in the system 100 to communicate with each other in order to perform theprocess of generating a mobile device-specific identifier usable acrossnative mobile applications and mobile browsers as described herein. Thenetwork 104 may be a local network, such as a LAN, and/or a wide areanetwork, such as the Internet and/or a cellular network, and/or acombination of a local network and a wide area network. In someembodiments, the network 104 is comprised of several discrete networksand/or sub-networks (e.g., cellular to Internet) that enable thecomponents of the system 100 to communicate with each other.

The system 110 also includes a database 114. The database 114 is coupledto service endpoint 106 and ad system 110 via the network 104, andstores data used by these components to perform the process ofgenerating a mobile device-specific identifier usable across nativemobile applications and mobile browsers as described herein. Thedatabase 114 can be integrated with one or more of the computing devicesof the system 100, or be located on a separate computing device ordevices. An example database that can be used with the system 100 isCouchbase available from Couchbase Inc. of Mountain View, Calif.

FIG. 2 is a flow diagram of a method 200 of generating a mobiledevice-specific identifier usable across native mobile applications andmobile browsers, using the system 100 of FIG. 1. The system 100generates (202) a transient identifier (TID) for the mobile device 102and maps the TID to a stable identifier (e.g., Device ID such as IDFA orAAID) of the mobile device 102 using at least one call to the serviceendpoint 106 coupled to the mobile device 102 via communications network104. The system 100 renders (204) a webpage in a browser application 103b on the mobile device 102. The webpage includes first instructions(e.g., Javascript code) that are executed by the browser application 103b, to retrieve the stable identifier of the mobile device 102 using atleast one call to the service endpoint 106. Further technical detailsregarding each of these steps 202, 204 are provided below.

Generating a Transient Identifier (TID)

As noted above, the first step is to generate (202) the TID for themobile device 102. The TIDs need to be sufficiently long-lived to allowan association with the device ID, and to tag websites visited by thebrowser 103 b of the mobile device 102. As presented herein, the system100 can generate TIDs without using cookies using a variety ofdevice-based fingerprinting techniques, of which three are describedbelow. These fingerprinting techniques can be used in isolation or incombination. Also, other fingerprinting approaches are possible and canbe used instead of, or in addition to, the techniques described below.

1) Generating a TID Based Upon DNS Caching

FIG. 3 is a ladder diagram 300 of a method of generating a TID basedupon a DNS Caching technique, using the system 100 of FIG. 1. In thebelow example, service endpoint 106 is reachable on one or moresubdomains id1.tiddns.com to id6.tiddns.com, a class C range of IPaddresses 1.2.3.0 to 1.2.3.255 is used by service endpoint 106, and aDNS server has been set up to return a random (or round-robin) addressin this IP range for every lookup on the following subdomains of theservice endpoint 106:

-   -   id1.tiddns.com    -   id2.tiddns.com    -   . . .    -   id6.tiddns.com

Therefore, when the mobile device 102 performs DNS resolution for theabove subdomains, the device 102 may get a result such as:

-   -   id1.tiddns.com→1.2.3.55    -   id2.tiddns.com→1.2.3.201    -   . . .    -   id6.tiddns.com→1.2.3.143        These values are illustrative and other values in the range of        IP addresses 1.2.3.0 to 1.2.3.255 may be returned by the DNS        server.

These lookups occur when the mobile device 102 accesses the serviceendpoint 106 on these subdomains. For instance, the mobile device 102can resolve the IP address of id1.tiddns.com (302) as part of opening aconnection and sending an HTTP GET request on id1.tiddns.com; in analternate embodiment, other types of HTTP requests (e.g., HTTP POST) maybe used. The native application 103 a or the browser 103 b of the mobiledevice 102 first resolves (302) “id1.tiddns.com” to “1.2.3.55,”establishes a connection with service endpoint 106 at this IP address,then sends (304) an HTTP GET request to the service endpoint 106. Theservice endpoint 106, which listens for requests on the entire IP range1.2.3.0 to 1.2.3.255, returns a snippet of Javascript that communicatesback to Javascript code running in the native application 103 a or thebrowser application 103 b on the mobile device 102 the lower 8-bits ofthe IP address (e.g., “55” in the above example). The same serviceendpoint implementation can be used for all subdomains id1 to id6—i.e.,the mobile device 102 repeats (306) the steps 302 and 304 above for eachremaining subdomain id2 to id6.

Once the mobile device 102 has called the six endpoints, the device 102stitches together (308) the six 8-bit values returned by the serviceendpoint 106 (e.g., “55,” “201,” . . . , “143” in the example above) togenerate a 48-bit TID (e.g., 0x37C9 . . . 8F in this example). Onsubsequent requests to the service endpoint 106, the mobile device 102uses the DNS resolution results that have been cached by its operatingsystem. This means that, as long as the DNS cache entries are stable onthe device 102, the device 102 calls the endpoints on the same IPs onsubsequent calls and thus receives the same results, allowing the device102 to stitch together the same TID. Because the DNS cache may be usedacross all applications on the device 102, the same TID can be retrievedboth from the native application 103 a and from different instances ofthe mobile browser 103 b (such as webviews). This is the case, forinstance, in Apple's iOS™

It should be appreciated that the DNS server should set the time-to-live(TTL) value of the returned A records to a sufficiently high value(e.g., one day) to ensure a sufficient lifetime for the TID. Because theDNS cache of the mobile device 102 may be flushed from time to time(e.g. on Apple's iOS™, whenever the device 102 goes into airplane mode,or whenever it switches between network interfaces), the TTL should beset to a value that is higher than the median time between these typesof events.

In an alternate embodiment, a different number of subdomains can be usedto generate TIDs of a different length. In an alternate embodiment, theservice endpoint 106 can use a class B range of IPs to reduce the numberof calls to the service endpoint 106, as each call could generate 16bits of information; for instance, with a class B range, only threesubdomains and three service endpoint calls are needed to generate a48-bit TID.

a) Avoiding Intermediary DNS Server Caches

Also, the system 100 should avoid intermediary DNS server caches (suchas those provided by a mobile carrier or a corporation) as part of theDNS Caching technique. In one example, the DNS lookup from the mobiledevice 102 does not necessarily go directly to the DNS server for theservice endpoint 106. For instance, a carrier/provider/corporation DNSserver may sit in between the mobile device 102 and the service endpoint106. Such intermediate DNS servers also cache the returned Arecords—which poses a problem if multiple mobile devices go through thesame DNS server, as all of these devices may get the same TIDs. To avoidthis, the system 100 can generate a stable, device-specific FingerprintID (FID) with a sufficient number of bits. The actual cardinality neededdepends on how many devices are expected to be sitting behind each DNScache and an acceptable collision rate. This FID could, for instance, begenerated based on the TCP timestamp of the device or the IP address ofthe device (as described below); additionally, the system 100 can alsouse e.g. the model, OS version, and language setting of the mobiledevice 102. Other fingerprinting approaches are possible and can be usedinstead of, or in addition to, these techniques.

Each device i now generates its own FIDi, and uses it to look up thefollowing device-specific subdomains instead:

-   -   FIDi.id1.tiddns.com→1.2.3.55    -   FIDi.id2.tiddns.com→1.2.3.201    -   . . .    -   FIDi.id6.tiddns.com→1.2.3.143

This technique creates different entries, one per device i anddevice-specific subdomain FIDi.id1.tiddns.com, . . .FIDi.id6.tiddns.com, in all intermediate DNS servers that may be cachingthe result; therefore, the probability of a collision is reduced,assuming the FIDs are sufficiently unique to differentiate between themobile devices using the same intermediate DNS server.

In one embodiment, the FID is generated based on the IP address of themobile device 102. In one embodiment, the FID is a hash of the externalIP address of the mobile device 102. In one embodiment, the external IPaddress of the mobile device 102 is obtained by calling a serviceendpoint 106 that returns the source IP address of the connection.

In one embodiment, the FID is not prepended to the subdomainsid1.tiddns.com . . . id6.tiddns.com of the service endpoint 106 togenerate device-specific subdomains; the mobile device 102 performs DNSresolution on these subdomains as described above; stitches together thevalues to obtain a first TID as described above; and appends a FID tothe first TID to generate a second TID. The second TID may be uniqueeven if the first TID is the same across mobile devices 102 sharing thesame DNS cache.

b) Avoiding Proxies

In addition, if the mobile device 102 accesses the internet via a proxy(such as a transparent proxy operated by a mobile carrier or acorporation), then the DNS lookups described above may be done by theproxy and not directly by the mobile device. In order to avoid this, themobile device 102 needs to send the requests to the service endpoint 106via HTTPS, which bypasses the proxies (at least for transparentproxies). In one implementation, wildcard TLS certificates for*.id1.tiddns.com . . . *.id6.tiddns.com need to be installed on theservice endpoint 106 to be able to serve requests over HTTPS forsubdomains such as:

-   -   FIDi.id1.tiddns.com    -   FIDi.id2.tiddns.com    -   . . .    -   FIDi.id6.tiddns.com

This allows the service endpoint 106 to authenticate properly to HTTPSrequests on FIDi.idj.tiddns.com.

c) Other DNS Caching Techniques

In some embodiments, the mobile device 102 uses the subdomains initiallydescribed:

-   -   id1.tiddns.com    -   id2.tiddns.com    -   . . .    -   id6.tiddns.com

But, the resulting TID may not be unique for devices using the same DNScache, as described above. Uniqueness can be achieved by combining theresulting TID with a second fingerprint TID′ (such as the one based onthe TCP timestamp approach described below) to form a unique fingerprint(TID, TID′) on the mobile device 102.

In an alternate implementation, the mobile device 102 only calls serviceendpoint 106 on the id1.tiddns.com subdomain. The service endpoint 106extracts the lower 8-bits of the IP address, then issues an HTTP 302redirect code that causes a redirect to the id2.tiddns.com subdomain,with the lower 8-bits of the IP address passed as a parameter in thequery string of the URL. For instance, the response of the serviceendpoint 106, when called on the first subdomain, may be the following:

-   -   HTTP/1.1 302 Found    -   Location: http://id2.tiddns.com?id1=55

Similarly, the service endpoint 106, when called on the id2.tiddns.comsubdomain, extracts the lower 8-bits of the IP address, then appendsthis value as a second parameter and redirects to the next subdomainid3.tiddns.com. For instance, the response of the service endpoint 106,when called on the second subdomain, may be the following:

-   -   HTTP/1.1 302 Found    -   Location: http://id3.tiddns.com?id1=55&id2=201

The sequence of redirects continues through each subdomain until theid6.tiddns.com subdomain is redirected to. When called on thissubdomain, the service endpoint 106 extracts the lower 8-bits of the IPaddress, uses the parameters in the query string to assemble the full48-bit TID, and returns this TID to the mobile device 102 as a snippetof Javascript.

2) Generating a TID Based Upon IPv6 Addresses

Another approach to generating a TID is to use IPv6 addresses. The lower64-bits of an IPv6 address may be derived from the MAC address of themobile device 102. To prevent disclosing the MAC address, most modernoperating systems implement RFC 4941 (Privacy Extensions)—these devicesgenerate a random 64-bit component and rotate this value once a day(typically).

The system 100 can implement an IPv6-based TID as follows. A serviceendpoint (e.g., 106) is exposed and accessible over IPv6 on thefollowing domain:

-   -   tidv6.com

The mobile device 102 can access this service endpoint, which simplyreturns the lower 64-bits of the mobile device's IPv6 address. This TIDis stable until the mobile device 102 rotates the lower 64-bits in itsIPv6 (typically, once a day) or until the mobile device 102 switches toa different network.

3) Generating a TID Based Upon a TCP Timestamp

Another approach to generating a TID is to use TCP timestamps. FIG. 4 isa ladder diagram of a method of generating a TID based upon TCPtimestamp technique, using the system 100 of FIG. 1.

RFC 1323 and RFC 7323 have defined TCP extensions for high performance.The original purpose of these RFCs is to provide PAWS (ProtectionAgainst Wrapped Sequences) and improve handling of “long, fat networks”(LFNs) by allowing round-trip time measurement (RT™).

TCP stacks that implement RFC 1323—“TCP Extensions for High Performance(https://www.ietf.org/rfc/rfc1323.txt) and RFC 7323—“TCP Extensions forHigh Performance” (https://tools.ietf.org/html/rfc7323)—such as the onein Apple's iOS™—include a TCP Timestamp Option (TSopt) in the TCPpackets they send. This option carries two fields as its payload: cf.RFC 1323 and RFC 7323 “TCP Extensions for High Performance”)

-   -   TS Value (TSval): this value monotonically increments with the        wall clock time on the mobile device 102. For instance, on        Apple's iOS™, TSval is initialized with a random 30-bit seed RS        when the device boots up, and the TSval sent is the random seed        plus the current device time, measured for the periods during        which the mobile device 102 is not sleeping.    -   TS Echo Reply (TSecr): this echoes the TSval last seen from the        other end of the TCP connection. A receiver can use TSecr to        compute an approximation of the connection latency L.

Because the TSval is initialized with a random seed (RS) that is uniqueto an OS instance (boot) on a device, RS or a value derived from it canbe used as a TID for the mobile device 102.

To extract this TID, the mobile device 102 calls the service endpoint106, for instance by performing a GET request on the following domain:

tidtsval.com

The mobile device 102 first opens a TCP connection to tidtsval.com(402). The service endpoint 106 extracts (404) TSval and TSecr from theTCP packets received over the TCP connection, and computes (406) a TIDthat represents an approximation of the random seed RS. The mobiledevice 102 sends an HTTP GET request (408) to the service endpoint 106over the connection. The service endpoint 106 returns (410) the TID (orJavascript code that contains the TID) to the mobile device 102 as theresult of the GET. In one embodiment, the service endpoint 106implements the extraction of TSval and TSecr as code running on a loadbalancer that inserts these values as part of special headers of theHTTP request forwarded to one of one or more servers. In oneimplementation, TID can be computed in step 406 as follows:TID=LoadBalancerWallClockTime−Tsval

Assuming the mobile device clock and the load balancer clock arereasonably synchronized and the drift is low, this provides anapproximation of RS that should be stable across multiple calls to theservice endpoint 106.

In an alternate implementation, the connection latency may also be usedto reduce imprecision due to latency jitter:TID=LoadBalancerWallClockTime−Tsval−L

In an alternate implementation, the system can bucketize the TID valuesto further reduce noise, and the service endpoint 106 returns theidentifier of the bucket, TID_(bucket):TID_(bucket)=Bucketize(TID)

One type of bucketization that works well in practice for iOS™ devices(based upon observation of a large traffic sample) is to subdivide theuseful 30-bit range of TID into 4096 buckets, thus to calculateTID_(bucket) by dividing the TID by 2¹⁸ which is the size of a bucket.This can be achieved by simply shifting the TID right by 18 bits:TID_(bucket)=TID»18

It should be appreciated that other types of bucketization are possiblefor use with the techniques described herein.

In an alternate implementation, the call from the mobile device 102 tothe service endpoint 106 is done over HTTPS in order to circumventtransparent proxies on port 80, such as the ones that may be provided bymobile carriers or corporations.

In an alternate implementation, the service endpoint 106 has a blacklistcontaining IP addresses. The service endpoint 106 can filter outrequests from IP addresses contained in the blacklist to avoid returningthe same TID to multiple devices, which would cause TID collisions. Inone embodiment, the blacklist contains IP addresses that generatesubstantial amounts of traffic with the same transient identifiers;corresponding to, e.g., mobile devices behind the same proxy, orfraudulent traffic.

In an alternative implementation, the TID value computed in step 406 bythe service endpoint 106 may be associated with the source IP address ofthe connection established in step 402 to reduce the number ofcollisions. Using the TID computed via one of the above TCP timestampapproaches, the value TID₁ returned by the service endpoint 106 is theconcatenation of the TID and the IP address:TID_(IP)=(TID,IP)

This approach helps reduce the number of collisions, as collisions cannow only occur between mobile devices sharing the same IP address (suchas devices going through the same NAT), not between all the devices onthe Internet.

Mapping the Transient Identifier to a Stable Device Identifier

Turning back to FIG. 2, once the system 100 generates TIDs as describedabove, the system maps (202) these TIDs to a stable device identifier,such as the Device ID described above (i.e., IDFA or AAID). Generally,the system can perform this mapping in several ways as described below;it should be appreciated that these approaches can be used in isolationor in combination with each other:

-   -   Using in-app support via an SDK embedded in the native        application 103 a;    -   Using a tracking pixel that is called from the native        application 103 a; and    -   Using an ad buying platform such as ad system 110 to buy and        display an ad impression in the native application 103 a.

These approaches use a service endpoint that stores and retrieves themapping between TID and Device ID; the service endpoint may be calledfrom the native application 103 a or from the mobile browser 103 b toestablish the mapping, and from the mobile browser 103 b to retrieve themapping—as is described in detail below.

In one embodiment, the mapping between TID and Device ID is stored indatabase 114; in one embodiment, the mapping is accessed by both theservice endpoint 106 and ad system 110.

In one embodiment, the service endpoint 106 is providing the service onthe following domain:

-   -   associate.stableid.com

and the service endpoint 106 exposes its functionality over HTTP orHTTPS. In one implementation, this could be implemented as a RESTfulAPI. The service endpoint 106 can be called from either the nativeapplication 103 a or from the mobile browser 103 b in the mobile device102 using Javascript.

The service endpoint 106 implements the following API:

-   -   associate: (TID, DeviceID)→DeviceID′

The service endpoint 106 is called with two parameters: the TID andDeviceID. In some cases, the DeviceID parameter can be null. In somecases, the TID is not passed explicitly, but can be extracted by theservice endpoint 106 using one of the methods described above, or usingsome other fingerprinting method. The service endpoint 106 returns aDeviceID′ if a mapping can be established, or null otherwise. In mostcases, DeviceID′, DeviceID but there are some cases described belowwhere this is not the case. In some implementations, aDeviceID′≠DeviceID is returned when a potential TID collision isdetected.

The service endpoint 106 keeps a mapping between TID and DeviceID. Inone implementation, the mapping between TID and DeviceID is stored indatabase 114; in one implementation, the database 114 is implemented asan in-memory cache such as Redis, memcached, or Couchbase.

When the service endpoint 106 is called with (TID, DeviceID) bothnon-null, the endpoint 106 updates its mapping table and returns theDeviceID′=DeviceID. Each entry <TID, DeviceID> in the mapping table canhave an expiration time after which the entry is automatically deleted.Updating an entry sets a new expiration time. As mentioned above, insome cases, the service endpoint 106 may return DeviceID′ DeviceID.

When the service endpoint 106 is called with (TID, null), the serviceendpoint 106 checks whether a non-expired entry <TID, DeviceID> existsin its mapping table. If an entry is found, the service endpoint 106returns DeviceID′=DeviceID; otherwise, it returns null.

1) Mapping Via In-App Support

In one instance, the system 100 can create the mapping between TID andDevice ID using a native application 103 a installed on the mobiledevice 102. The native application 103 a is instrumented with codeimplementing the functionality described below to facilitate theassociation between TID and DeviceID. In one implementation, this codeis included in a dedicated application 103 a. In an alternateimplementation, the code is contained in an SDK that is included in atleast one native application 103 a installed on the mobile device. In analternate implementation, the code is executed in an instance of themobile browser 103 b created by the native application 103 a.

The code listens for “interesting” system events that could indicatethat the <TID, DeviceID> mapping has changed. These events include, butare not limited to: device reboot; device waking from sleep; devicenetwork interface change; certain time interval has elapsed (e.g.,periodic refresh); airplane mode has been disabled in the device; or theWiFi connection on the device has been re-enabled.

Upon detection of one or more of these events, the code in the mobiledevice 102 executes the following steps (as shown in FIG. 5):

1) Retrieve (502) the DeviceID for the mobile device 102 by calling theappropriate mobile device API; for instance, on Apple's iOS™ this can bedone by accessing the shared instance of the ASIdentifierManager class.If the retrieved DeviceID is null, meaning that Device ID sharing hasbeen turned off, do nothing; otherwise continue to the next step.

2) Retrieve (504) the TID for the mobile device 102 by using one of themethods described above. If the TID cannot be retrieved, do nothing;otherwise continue to the next step. In an alternate implementation, theTID is retrieved directly by the service endpoint 106 when it is calledin step 506.

3) Call (506) the service endpoint 106 with arguments (TID, DeviceID).The result of the call is ignored; as part of processing the call, theservice endpoint 106 updates its mapping as described above.

2) Mapping Via In-App Advertisements

In another instance, the service endpoint 106 has access to ad system110 and can leverage displaying in-app advertisements in the nativeapplication 103 a on the mobile device 102 to set and update the <TID,DeviceID> mapping. This approach is performed by buying an ad impressionin-app, either through a real-time bidding platform (RTB) 112 or viadirect in-app inventory in the native application 103 a. The adimpression served by, e.g., ad system 110 contains Javascriptinstrumentation that implements the following functionality when theadvertisement is displayed in the native application 103 a (as shown inFIG. 6):

1) Retrieve (602) the TID for the mobile device 102 by using one of themethods described above. If the TID cannot be retrieved, do nothing;otherwise, continue to the next step.

2) Retrieve (604) the Device ID for the mobile device 102. Because adsdisplayed in the native application 103 a typically contain HTML andJavascript, the native application 103 a may use an instance of thebrowser application 103 b to render ads; as such, the DeviceID cannot beretrieved directly from within the instance of the browser application103 b, but needs to be passed as part of the Javascript code or URL ofthe advertisement, and extracted by the Javascript code of the ad.

3) Call (606) the service endpoint 106 with arguments (TID, DeviceID),from the Javascript code of the ad. The result of the call is ignored;as part of processing the call, the service endpoint updates its mappingas described above.

In one implementation, the ad impression is bought in the normal courseof targeting the user of the mobile device 102 (via the Device ID) aspart of an advertisement campaign. For instance, ad system 110 may havedetected previous in-app activity on the mobile device 102 and maydecide to show an advertisement to the user of that device.

In an alternative implementation, the ad impression is bought based onwhether a non-expired mapping exists in the mapping table containing thegiven DeviceID. When a display opportunity is detected for a nativeapplication 103 a running on the mobile device 102 with this Device ID,the following steps are performed (as shown in FIG. 7):

1) Identify (702) whether a non-expired mapping exists. If a non-expiredmapping <TID, DeviceID> exists in the mapping table, do nothing;otherwise continue to the next step.

2) Bid (704) for the ad impression. In some embodiments, the bid isplaced in response to a bid request sent by RTB platform 112, where saidbid request contains the DeviceID. In some embodiments, the bid price isdetermined by ad system 110. In one implementation, the bid price is thefloor price for the ad impression opportunity.

In an alternative implementation, an ad impression is bought wheneverthe IP address on which the DeviceID is seen in a bid request differsfrom the one on which it was seen last in another bid request; in thiscase, the IP address needs to be included in the mapping <TID, DeviceID,IP> stored in database 114. A change of IP address may be an indicationthat the device TID has changed, and the mapping needs to be updated.

3) Mapping Via In-App Pixels

In another instance, the system 100 can create the mapping between TIDand Device ID using pixels called from a native application 103 ainstalled on the mobile device 102. For example, several companies thatprovide in-app SDKs may inject impression pixels. These impressionpixels are generally configured by the publisher in the ad server UI anddo not need any SDK update. The pixels can be called with the Device IDas a parameter by using the corresponding macro that is provided by thein-app ad server; for instance, on the Google™ SDK, the DeviceID can beobtained via the %% ADVERTISING_IDENTIFIER_PLAIN %% macro.

One or more ad server UIs can therefore be used to inject an impressionpixel that calls a pixel corresponding to a service endpoint 106:

-   -   tidassociate.stableid.com

The service endpoint 106 computes the TID (for instance, using one ofthe methods described above) and associates it to the Device ID byupdating its mapping as described above. The tidassociate APIfunctionality is the composition of one of the tidxxx endpointsdescribed above (e.g., tidtsval) and the associate endpoint describedabove:

-   -   tidassociate: (DeviceID)—DeviceID′

The system 100 can perform the computation of the TID using any of theapproaches previously described herein.

Using the Stable Device Identifier in the Mobile Browser

Turning back to FIG. 2, after the TID has been generated and mapped to astable identifier (i.e., Device ID) as described above (202), thebrowser application 103 b of the mobile device 102 can retrieve thestable identifier during rendering (204) of a webpage using at least onecall to a service endpoint 106. The browser application 103 b can thenuse the retrieved stable identifier to, e.g., store it as alocally-stored value (e.g., by dropping first-party cookies, orthird-party cookies), include the identifier in browser-based bidrequests, and the like—as will be described in greater detail below.

To obtain the stable identifier for the mobile device 102, uponrendering a web page, the browser application 103 b executes in the webpage Javascript code that performs the following (as shown in FIG. 8):

1) Retrieve (802) the TID by using one of the methods described above.If the TID cannot be retrieved, do nothing; otherwise, continue to thenext step. In an alternate implementation, the TID can be retrieved bythe service endpoint 106 when the service endpoint 106 is called in step806, and the TID does not need to be explicitly retrieved by theJavascript code.

2) If a locally-stored value (such as a first-party cookie) containingthe DeviceID exists on the current domain of the web page, retrieve (804a) the DeviceID; otherwise, set (804 b) DeviceID to null. Types oflocally-stored values can include, but are not limited to: a first-partycookie, a third-party cookie, a partitioned third-party cookie, abrowser cache, a partitioned browser cache, or local storage.

3) Call (806) the service endpoint 106 with arguments (TID, DeviceID).If no result can be retrieved by the service endpoint 106, do nothing.Otherwise, assume the result is DeviceID′.

4) If a locally-stored value can be set; if DeviceID′, null, clear (808)any existing locally-stored value containing a DeviceID; otherwise, set(810) the locally-stored value containing DeviceID′.

Note that the above example code stores the DeviceID as a locally-storedvalue for all domains on which the Javascript is executed. Initially, nosuch locally-stored values exist for these domains, but as the initialmapping between TID and DeviceID is established, it is stored in such alocally-stored value. This means that in one embodiment, on subsequentvisits to this domain, the DeviceID contained in the locally-storedvalue can be used to establish a mapping with the TID when the serviceendpoint is called, as described above.

In some cases, the service endpoint 106 may return a DeviceID′ that isdifferent from the DeviceID contained in the locally-stored value. Thismay happen if there was a collision on a TID previously, which resultedin the wrong DeviceID being stored in the locally-stored value. Theservice endpoint 106 decides which DeviceID is authoritative and forcesan update of the locally-stored value. In one implementation, thisdecision may be based at least in part on a timestamp.

Also, it should be appreciated that the Javascript code described abovecan be included as part of a tag on retailer, brand, or publisher pages.

1) Using the Stable Identifier to Bid for Mobile Browser Impressions

Ad inventory available on pages rendered by the browser application 103b can be sold via the RTB platform 112 that is connected to ad system110. For example, ad system 110 can use the user identity passed in abid request by the RTB platform 112 to decide whether, and how much, tobid for an impression based on the value of that user.

In some embodiments, the user identity is either specific to the RTBplatform 112, or to ad system 110, if a mapping (e.g., a cookie sync)has been established previously between ad system 110 and the RTBplatform 112. Normally, the RTB platform 112 stores this identity as acookie on its own RTB domain, i.e. a third-party cookie relative to thedomain of the web server 108.

However, as mentioned previously, with the ITP functionality in place onApple's iOS™, RTB domains associated with RTB platforms may beclassified as ‘trackers’ and as such, the RTB platform 112 may not beable to store the user identity in a third-party cookie. To overcomethis drawback, the system 100 can include Javascript code as part of anad impression opportunity that is executed by the mobile browserapplication 103 a and performs the following (as shown in FIG. 9):

1) Retrieve (902) the TID by using one of the methods described above.If the TID cannot be retrieved, do nothing; otherwise, continue to thenext step. In an alternate implementation, the TID can be retrieved bythe service endpoint 106 when the service endpoint 106 is called in step906, and the TID does not need to be explicitly retrieved by theJavascript code.

2) If a locally-stored value containing the DeviceID exists for thecurrent domain of the web page containing the ad impression (e.g., thedomain of the web server 108), retrieve (904 a) the DeviceID from thelocally-stored value; otherwise, set (904 b) the DeviceID to null.

3) Call (906) the service endpoint 106 with arguments (TID, DeviceID).If no result is retrieved, do nothing. Otherwise, assume the result isDeviceID′.

4) If DeviceID′ is null, clear (908) any locally-stored values andcontinue with step 6 below; if DeviceID′ is not null, continue to thenext step.

5) If a first-party locally-stored value can be set for the currentdomain of the web page containing the ad impression, set (910) thelocally-stored value containing DeviceID′ and continue to the next step;otherwise, do nothing and continue to the next step.

6) Pass (912) the DeviceID′ to the RTB platform 112. In turn, the RTBplatform 112 may pass the DeviceID′ as part of the bid request, to adsystem 110.

This approach allows ad system 110 to receive the Device ID and bidsmartly, for domains on which the Device ID can be retrieved.

In an alternate implementation, the DeviceID is only passed to the RTBplatform 112 if a locally-stored value has been set previously (withoutcalling the service endpoint 106), thus the following steps areexecuted:

1) If a locally-stored value containing the DeviceID exists for thecurrent domain of the page containing the impression, retrieve theDeviceID; otherwise, set DeviceID to null.

2) Pass the DeviceID to the RTB platform 112. In turn, the RTB platform112 may pass the DeviceID as part of the bid requests, to ad system 110.

2) Protecting User Privacy

In one implementation, the content of the locally-stored value is theDeviceID itself.

However, because third parties may be able to access and use thelocally-stored values, it is important to protect user privacy andprevent such use by third parties. In an alternate implementation, thelocally-stored value does not contain the DeviceID itself, but a valuederived from it—called a Secure Identifier (SID). The generation of aSID is described below.

In this example, the system uses a secret symmetric encryption key (KS)held by the service endpoint 106. The system can generate a secureidentifier from a DeviceID as follows:SID={timestamp, salt, DeviceID}|_(KS)

i.e. the SID is the encrypted value of the concatenation of the currenttime (timestamp), a random salt of sufficient cardinality (for instance,a 256-bit salt), and the DeviceID.

A SID can be decrypted by the service endpoint 106, using KS, toretrieve the timestamp and the DeviceID. The salt is discarded afterdecryption.

In addition to the service endpoint 106 functionality describedpreviously, the service endpoint 106 provides a second API that iscalled from mobile browsers 103 b on, e.g., the following domain:

-   -   secureassociate.stableid.com

The signature of this API is similar to that of the associate API, withthe difference that SIDs are passed and returned instead of ‘plaintext’DeviceIDs; namely:

-   -   secureassociate: (TID, SID)→SID′

Using the secureassociate API, the browser application 103 b sets orobtains the SID′ corresponding to the current TID—similar to theapproach described above. In this instance, the SID′ is stored in thelocally-stored value, and rotates—or changes—due to different timestampsused to generate it, every time secureassociate is called. The SID doesnot divulge the underlying Device ID and is unusable by third-parties,because the timestamp and random salt cause the SID to rotate on eachcall and help thwart brute-force attacks.

In one implementation, the SID is passed to the RTB platform 112 as partof an ad impression opportunity, as described above; the RTB platformpasses the SID as part of its bid request to ad system 110; and adsystem 110, sharing the key KS with the service endpoint 106, candecrypt the SID to extract the Device ID.

In one embodiment, the key KS is stored in database 114; in oneembodiment, KS can be accessed by the service endpoint 106, and adsystem 110.

Implementing a Unified Opt-Out Mechanism Across Mobile Applications andBrowsers

Based upon the above-described techniques for generating a TID, mappingthe TID to a stable device identifier, and using the stable identifierin mobile browser applications 103 b, the system 100 can implement anadvantageous unified opt-out mechanism for both native mobileapplications 103 a and mobile browsers 103 b using the Device ID sharingfunctionality of the mobile device 102 currently used only for optingout of native app advertisements. The mobile browser opt-out mechanismdescribed herein takes effect eventually, after a maximum time (e.g., 48hours or 72 hours) has elapsed since the Device ID sharing has beenturned off or disabled on the mobile device 102.

To achieve the unified opt-out mechanism, the service endpoint 106 andad system 110 maintain a second mapping of ‘last seen’ times for eachDeviceID, as follows:

-   -   lastseen: DeviceID→timestamp

In one embodiment, the second mapping is stored in database 114; in oneembodiment, the second mapping can be accessed and updated by theservice endpoint 106 and ad system 110.

The receiving of the DeviceID by ad system 110 in an in-app RTB bidrequest issued by the RTB platform 112, or by the service endpoint 106in an associate or secureassociate API call initiated from a nativeapplication 103 a, using one of the methods described above, is areliable indication that Device ID sharing has not been disabled on themobile device 102. In these cases, ad system 110 or the service endpoint106, respectively, updates the timestamp in the lastseen mapping for theDeviceID to the current time. The lastseen mapping entry is set toexpire after a maximum time (for instance, 48 hours or 72 hours).

If the user disables DeviceID sharing on his or her mobile device 102,the lastseen mapping table will not contain a valid mapping for theDeviceID after the maximum time, because any such mapping (if it existedbefore) is now expired; the mapping will not be renewed until after theuser re-enables Device ID sharing on his or her mobile device 102,because the mobile device 102 stops transmitting the DeviceID until suchevent.

When a mobile browser ad display opportunity is seen, ad system 110 orservice endpoint 106 checks whether a lastseen mapping exists for theDeviceID (or SID, as described above) passed as part of the ad displayopportunity (for a direct publisher relationship) or the RTB bid requestissued by RTB platform 112. If a SID is passed, it is first decrypted asdescribed above to extract the DeviceID. If no mapping exists in thelastseen second mapping table, or an expired mapping exists, this meansthat the DeviceID has not been seen recently and it is likely the userhas opted out by disabling the DeviceID sharing on the mobile device102. In that case, ad system 110 does not make a bid for the underlyingad impression, and thus the user is not subsequently targeted orretargeted.

In one embodiment, opt-out can be reverted when the user re-enablesDevice ID sharing on his or her mobile device 102. Following thisre-enabling, the DeviceID will eventually be seen in an in-app RTB bidrequest sent by the RTB platform 112 or in an associate orsecureassociate API call initiated from a native app 103 a; the secondmapping will be updated; and the user can again be targeted orretargeted.

The above-described techniques can be implemented in digital and/oranalog electronic circuitry, or in computer hardware, firmware,software, or in combinations of them. The implementation can be as acomputer program product, i.e., a computer program tangibly embodied ina machine-readable storage device, for execution by, or to control theoperation of, a data processing apparatus, e.g., a programmableprocessor, a computer, and/or multiple computers. A computer program canbe written in any form of computer or programming language, includingsource code, compiled code, interpreted code and/or machine code, andthe computer program can be deployed in any form, including as astand-alone program or as a subroutine, element, or other unit suitablefor use in a computing environment. A computer program can be deployedto be executed on one computer or on multiple computers at one or moresites.

Method steps can be performed by one or more specialized processorsexecuting a computer program to perform functions by operating on inputdata and/or generating output data. Method steps can also be performedby, and an apparatus can be implemented as, special purpose logiccircuitry, e.g., a FPGA (field programmable gate array), a FPAA(field-programmable analog array), a CPLD (complex programmable logicdevice), a PSoC (Programmable System-on-Chip), ASIP(application-specific instruction-set processor), or an ASIC(application-specific integrated circuit), or the like. Subroutines canrefer to portions of the stored computer program and/or the processor,and/or the special circuitry that implement one or more functions.

Processors suitable for the execution of a computer program include, byway of example, special purpose microprocessors. Generally, a processorreceives instructions and data from a read-only memory or a randomaccess memory or both. The essential elements of a computer are aprocessor for executing instructions and one or more memory devices forstoring instructions and/or data. Memory devices, such as a cache, canbe used to temporarily store data. Memory devices can also be used forlong-term data storage. Generally, a computer also includes, or isoperatively coupled to receive data from or transfer data to, or both,one or more mass storage devices for storing data, e.g., magnetic,magneto-optical disks, or optical disks. A computer can also beoperatively coupled to a communications network in order to receiveinstructions and/or data from the network and/or to transferinstructions and/or data to the network. Computer-readable storagemediums suitable for embodying computer program instructions and datainclude all forms of volatile and non-volatile memory, including by wayof example semiconductor memory devices, e.g., DRAM, SRAM, EPROM,EEPROM, and flash memory devices; magnetic disks, e.g., internal harddisks or removable disks; magneto-optical disks; and optical disks,e.g., CD, DVD, HD-DVD, and Blu-ray disks. The processor and the memorycan be supplemented by and/or incorporated in special purpose logiccircuitry.

To provide for interaction with a user, the above described techniquescan be implemented on a computer in communication with a display device,e.g., a CRT (cathode ray tube), plasma, or LCD (liquid crystal display)monitor, for displaying information to the user and a keyboard and apointing device, e.g., a mouse, a trackball, a touchpad, or a motionsensor, by which the user can provide input to the computer (e.g.,interact with a user interface element). Other kinds of devices can beused to provide for interaction with a user as well; for example,feedback provided to the user can be any form of sensory feedback, e.g.,visual feedback, auditory feedback, or tactile feedback; and input fromthe user can be received in any form, including acoustic, speech, and/ortactile input.

The above described techniques can be implemented in a distributedcomputing system that includes a back-end component. The back-endcomponent can, for example, be a data server, a middleware component,and/or an application server. The above described techniques can beimplemented in a distributed computing system that includes a front-endcomponent. The front-end component can, for example, be a clientcomputer having a graphical user interface, a Web browser through whicha user can interact with an example implementation, and/or othergraphical user interfaces for a transmitting device. The above describedtechniques can be implemented in a distributed computing system thatincludes any combination of such back-end, middleware, or front-endcomponents.

The components of the computing system can be interconnected bytransmission medium, which can include any form or medium of digital oranalog data communication (e.g., a communication network). Transmissionmedium can include one or more packet-based networks and/or one or morecircuit-based networks in any configuration. Packet-based networks caninclude, for example, the Internet, a carrier internet protocol (IP)network (e.g., local area network (LAN), wide area network (WAN), campusarea network (CAN), metropolitan area network (MAN), home area network(HAN)), a private IP network, an IP private branch exchange (IPBX), awireless network (e.g., radio access network (RAN), Bluetooth, Wi-Fi,WiMAX, general packet radio service (GPRS) network, HiperLAN), and/orother packet-based networks. Circuit-based networks can include, forexample, the public switched telephone network (PSTN), a legacy privatebranch exchange (PBX), a wireless network (e.g., RAN, code-divisionmultiple access (CDMA) network, time division multiple access (TDMA)network, global system for mobile communications (GSM) network), and/orother circuit-based networks.

Information transfer over transmission medium can be based on one ormore communication protocols. Communication protocols can include, forexample, Ethernet protocol, Internet Protocol (IP), Voice over IP(VOIP), a Peer-to-Peer (P2P) protocol, Hypertext Transfer Protocol(HTTP), Session Initiation Protocol (SIP), H.323, Media Gateway ControlProtocol (MGCP), Signaling System #7 (SS7), a Global System for MobileCommunications (GSM) protocol, a Push-to-Talk (PTT) protocol, a PTT overCellular (POC) protocol, Universal Mobile Telecommunications System(UMTS), 3GPP Long Term Evolution (LTE) and/or other communicationprotocols.

Devices of the computing system can include, for example, a computer, acomputer with a browser device, a telephone, an IP phone, a mobiledevice (e.g., cellular phone, personal digital assistant (PDA) device,smart phone, tablet, laptop computer, electronic mail device), and/orother communication devices. The browser device includes, for example, acomputer (e.g., desktop computer and/or laptop computer) with a WorldWide Web browser (e.g., Chrome™ from Google, Inc., Microsoft® InternetExplorer® available from Microsoft Corporation, and/or Mozilla® Firefoxavailable from Mozilla Corporation). Mobile computing device include,for example, a Blackberry® from Research in Motion, an iPhone® fromApple Corporation, and/or an Android™-based device. IP phones include,for example, a Cisco® Unified IP Phone 7985G and/or a Cisco® UnifiedWireless Phone 7920 available from Cisco Systems, Inc.

Comprise, include, and/or plural forms of each are open ended andinclude the listed parts and can include additional parts that are notlisted. And/or is open ended and includes one or more of the listedparts and combinations of the listed parts.

One skilled in the art will realize the invention may be embodied inother specific forms without departing from the spirit or essentialcharacteristics thereof. The foregoing embodiments are therefore to beconsidered in all respects illustrative rather than limiting of theinvention described herein.

What is claimed is:
 1. A system for generating a mobile device-specificidentifier usable across native mobile applications and mobile browsers,the system comprising a mobile device that: generates a transientidentifier for the mobile device and maps the transient identifier to astable identifier of the mobile device using at least one call to aservice endpoint coupled to the mobile device via a communicationsnetwork; and renders a webpage in a browser application, the webpagecomprising first instructions, executed by the browser application, toretrieve the stable identifier of the mobile device using at least onecall to the service endpoint coupled to the mobile device via acommunications network; wherein said generating a transient identifierfor the mobile device and mapping the transient identifier to the stableidentifier of the mobile device using at least one call to a serviceendpoint comprises: establishing, by the mobile device, a plurality ofconnections to a second service endpoint, each connection on a differentsubdomain, wherein when establishing the plurality of connections, themobile device performs Domain Name System (DNS) resolution on eachdifferent subdomain to generate an IP address for the subdomain;generating, for each DNS resolution, by a DNS server associated to eachdifferent subdomain, an IP address for the associated subdomaincomprising a random subset of bits; extracting and returning, by thesecond service endpoint, the random subset of bits for each of theplurality of connections; generating, by the mobile device, thetransient identifier using at least one of the returned random subsetsof bits from each DNS resolution; retrieving, by the mobile device, thestable identifier of the mobile device; establishing, by the mobiledevice, a connection to the service endpoint; sending, by the mobiledevice, the stable identifier of the mobile device and the transientidentifier to the service endpoint; and storing, by the serviceendpoint, a mapping between the transient identifier and the stableidentifier of the mobile device.
 2. The system of claim 1, wherein thestable identifier is an iOS™ IDFA.
 3. The system of claim 1, wherein thestable identifier is an Android™ AAID.
 4. The system of claim 1, whereinthe retrieved stable identifier is based at least in part on alocally-stored value in the browser application.
 5. The system of claim1, wherein the webpage contains second instructions to track useractivity based on the retrieved stable identifier.
 6. The system ofclaim 5, wherein tracking user activity comprises capturing one or moreattributes associated with user activity on a website in the browserapplication.
 7. The system of claim 6, wherein user activity comprisesone or more of: a visit to a product webpage, a search for a product, avisit to a category webpage, an add-to-cart action, or a completion of atransaction.
 8. The system of claim 5, wherein the website is anecommerce retailer website.
 9. The system of claim 1, wherein thewebpage contains third instructions to identify the mobile device to anad server or an RTB platform based on the retrieved stable identifier,as part of a bid request associated with at least one ad impressionopportunity.
 10. The system of claim 1, wherein generating a transientidentifier for the mobile device and mapping the transient identifier tothe stable identifier of the mobile device using at least one call to aservice endpoint comprises: retrieving, by the mobile device, the stableidentifier of the mobile device; establishing, by the mobile device, aconnection to the service endpoint; sending, by the mobile device, thestable identifier to the service endpoint; generating, by the serviceendpoint, the transient identifier; and storing, by the serviceendpoint, a mapping between the transient identifier and the stableidentifier of the mobile device.
 11. The system of claim 10, whereinestablishing a connection to the service endpoint comprises:establishing, by the mobile device, a TCP connection to the serviceendpoint; and performing, by the mobile device, an HTTP request over theTCP connection.
 12. The system of claim 11, wherein generating thetransient identifier by the service endpoint comprises: extracting atleast one of TSval or TSecr from TCP timestamp options of at least oneTCP packet received from the mobile device over the TCP connection; andgenerating the transient identifier using at least one of TSval, TSecr,a clock time associated with the service endpoint, and a source IPaddress of the TCP connection.
 13. The system of claim 12, wherein theservice endpoint: determines a latency associated with the TCPconnection using TSecr and the clock time of the service endpoint; andgenerates the transient identifier using a concatenation of (i) thesource IP address and (ii) a difference between the clock time of theservice endpoint, TSval, and the latency associated with the TCPconnection.
 14. The system of claim 11, wherein generating the transientidentifier by the service endpoint comprises: identifying the sourceIPv6 address of the TCP connection; and generating the transientidentifier using the source IPv6 address.
 15. The system of claim 11,wherein the service endpoint: identifies the source IP address of theTCP connection; determines that the identified source IP address isincluded in a blacklist; and discards one or more requests from a mobiledevice associated with the identified source IP address.
 16. The systemof claim 15, wherein the blacklist contains one or more IP addressesthat generate substantial amounts of traffic with the same transientidentifier.
 17. The system of claim 16, wherein the one or more IPaddresses in the blacklist correspond to one or more proxies, or tofraudulent traffic.
 18. The system of claim 10, wherein establishing aconnection to the service endpoint comprises: establishing, by themobile device, a TCP connection to the service endpoint; and performing,by the mobile device, an HTTPS request over the TCP connection.
 19. Thesystem of claim 18, wherein generating the transient identifier by theservice endpoint comprises: extracting at least one of TSval or TSecrfrom TCP timestamp options of at least one TCP packet received from themobile device over the TCP connection; and generating the transientidentifier using at least one of TSval, TSecr, a clock time associatedwith the service endpoint, and a source IP address of the TCPconnection.
 20. The system of claim 19, wherein the service endpoint:determines a latency associated with the TCP connection using TSecr andthe clock time of the service endpoint; and generates the transientidentifier using a concatenation of (i) the source IP address and (ii) adifference between the clock time of the service endpoint, TSval, andthe latency associated with the TCP connection.
 21. The system of claim18, wherein generating the transient identifier by the service endpointcomprises: identifying the source IPv6 address of the TCP connection;and generating the transient identifier using the source IPv6 address.22. The system of claim 18, wherein the service endpoint: identifies thesource IP address of the TCP connection; determines that the identifiedsource IP address is included in a blacklist; and discards one or morerequests from a mobile device associated with the identified source IPaddress.
 23. The system of claim 22, wherein the blacklist contains oneor more IP addresses that generate substantial amounts of traffic withthe same transient identifier.
 24. The system of claim 23, wherein theone or more IP addresses in the blacklist correspond to one or moreproxies, or to fraudulent traffic.
 25. The system of claim 10, whereinthe service endpoint allocates the transient identifier to one of aplurality of buckets to generate an updated transient identifier. 26.The system of claim 25, wherein allocation to one of a plurality ofbuckets is achieved by dividing a value range of the transientidentifier into a number of equally-sized intervals, and computing afloor of the transient identifier divided by the size of an interval.27. The system of claim 26, wherein the number of buckets is
 4096. 28.The system of claim 1, wherein retrieving the stable identifier of themobile device using at least one call to the service endpoint comprises:establishing, by the mobile device, a connection to the serviceendpoint; generating, by the service endpoint, a first transientidentifier; retrieving, by the service endpoint, the stable identifierof the mobile device, using a mapping between the first transientidentifier and the stable identifier of the mobile device; and sending,by the service endpoint to the mobile device, the stable identifier ofthe mobile device.
 29. The system of claim 1, wherein the serviceendpoint and the second service endpoint are the same.
 30. The system ofclaim 1, wherein the plurality of connections to the second serviceendpoint is initiated by the mobile device.
 31. The system of claim 1,wherein a first of the plurality of connections to the second serviceendpoint is initiated by the mobile device and the rest of the pluralityof connections to the second service endpoint are controlled by thesecond service endpoint via redirects.
 32. The system of claim 1,wherein generating the transient identifier using each of the randomsubsets of bits from each DNS resolution comprises: identifying, by thesecond service endpoint for each connection, the IP address on which thesecond service endpoint is called; extracting, by the second serviceendpoint for each connection, the random subset of bits from the IPaddress; transmitting, by the second service endpoint for eachconnection, the random subset of bits to the mobile device; andconcatenating, by the mobile device, each of the random subsets of bitsreceived from the second service endpoint to generate the transientidentifier.
 33. The system of claim 1, wherein generating a transientidentifier for the mobile device and mapping the transient identifier tothe stable identifier of the mobile device using at least one call to aservice endpoint comprises: establishing, by the mobile device, aplurality of connections to a second service endpoint, each connectionon a different subdomain, wherein when establishing the plurality ofconnections, the mobile device performs Domain Name System (DNS)resolution on each different subdomain to generate an IP address for thesubdomain; generating, for each DNS resolution, by a DNS serverassociated to each different subdomain, an IP address for the associatedsubdomain comprising a random subset of bits; extracting, by the secondservice endpoint for the first connection, the random subset of bitsfrom the IP address; redirecting, by the second service endpoint, toeach of the other plurality of connections on a different subdomainsequentially, wherein on each redirection the second service endpointpasses the extracted random subsets of bits to the redirectedconnection, extracts the random subset of bits from the IP address ofthe redirected connection, and concatenates the extracted random subsetof bits to the passed extracted random subsets of bits to form aconcatenated value that forms a new extracted random subset of bits;using, by the second service endpoint, upon a last redirection, theconcatenated value as the generated transient identifier; retrieving, bythe mobile device, the stable identifier of the mobile device;establishing, by the mobile device, a connection to the serviceendpoint; sending, by the mobile device, the stable identifier of themobile device and the transient identifier to the service endpoint; andstoring, by the second service endpoint, a mapping between the transientidentifier and the stable identifier of the mobile device.
 34. Thesystem of claim 1, wherein the second service endpoint: identifies thesource IP address of each of the plurality of connections; determinesthat one or more of the identified source IP addresses is included in ablacklist; and discards one or more requests from a mobile deviceassociated with the identified source IP addresses.
 35. The system ofclaim 1, wherein the mobile device stores DNS resolution data comprisinga mapping of each subdomain to its corresponding IP address in a DNScache of the mobile device.
 36. The system of claim 1, wherein the DNSserver associated to each different subdomain sets a time-to-live (TTL)of the DNS resolution data to a predetermined value.
 37. The system ofclaim 36, wherein the predetermined value is at least one day.
 38. Thesystem of claim 1, wherein the random subset of bits from the IP addressfor the associated subdomain is at least 8 bits, corresponding to aclass C range of IP addresses.
 39. The system of claim 1, wherein therandom subset of bits from the IP address for the associated subdomainis at least 16 bits, corresponding to a class B range of IP addresses.40. The system of claim 1, wherein the mobile device: generates adevice-specific identifier for the mobile device; appends thedevice-specific identifier to each different subdomain to generatedevices-pecific subdomains that are one level deeper than each differentsubdomain; performs the DNS resolution using the device-specificsubdomains; and wherein the DNS server associated to each differentsubdomain generates, for each DNS resolution using the device-specificsubdomain, an IP address for the devicespecific subdomain comprising arandom subset of bits.
 41. The system of claim 1, wherein at least oneconnection between the mobile device and second service endpoint is anHTTPS connection.
 42. The system of claim 1, wherein the mobile device:generates a device-specific identifier for the mobile device; performsthe DNS resolution using each of the different subdomains; uses thesecond endpoint to generate a first transient identifier; and appendsthe device-specific identifier to the first transient identifier toobtain a second transient identifier.
 43. The system of claim 42,wherein the device-specific identifier for the mobile device isgenerated based on an IP address of the mobile device.
 44. The system ofclaim 43, wherein the device-specific identifier for the mobile deviceis a hash of an IP address of the mobile device.
 45. The system of claim43, wherein the mobile device obtains the IP address of the mobiledevice by calling a service endpoint that returns a source IP address.46. The system of claim 1, wherein the mobile device combines thetransient identifier received from the service endpoint with anothertransient identifier generated by the mobile device to form an updatedtransient identifier.
 47. The system of claim 1, wherein the mobiledevice combines the generated transient identifier with one or more dataelements associated with the mobile device to form an updated transientidentifier.
 48. The system of claim 47, wherein the one or more dataelements associated with the mobile device comprise at least one of: adevice model, a language setting, or a software version.
 49. The systemof claim 10, wherein the mapping comprises the transient identifier, thestable identifier, a mapping expiration time, and an identifier of amethod used to generate the transient identifier.
 50. The system ofclaim 49, wherein retrieving the stable identifier of the mobile device,using at least one call to the service endpoint, comprises: retrieving,by the service endpoint, the transient identifier; determining, by theservice endpoint, whether a non-expired mapping exists between thetransient identifier and the stable identifier; transmitting, by theservice endpoint, the stable identifier to the mobile device if anon-expired mapping exists; and transmitting, by the service endpoint, anull value to the mobile device if no mapping exists or if an expiredmapping exists.
 51. The system of claim 1, wherein generating atransient identifier for the mobile device and mapping the transientidentifier to a stable identifier of the mobile device is initiated byan SDK within a native application installed on the mobile device. 52.The system of claim 51, wherein generating a transient identifier forthe mobile device and mapping the transient identifier to a stableidentifier of the mobile device is initiated upon an occurrence of oneor more events detected by the SDK at the mobile device.
 53. The systemof claim 52, wherein the one or more events comprise a reboot of themobile device, a waking from sleep of the mobile device, a networkinterface change of the mobile device, a connectivity change of themobile device, or an elapsing of a predetermined time interval.
 54. Thesystem of claim 1, wherein generating a transient identifier for themobile device and mapping the transient identifier to a stableidentifier of the mobile device is initiated by code associated with anad impression rendered in a native application installed on the mobiledevice.
 55. The system of claim 54, wherein the stable identifier isembedded within the code associated with the ad impression and themobile device extracts the stable identifier for transmission to theservice endpoint as part of the call to the service endpoint.
 56. Thesystem of claim 55, wherein the stable identifier is included in an URLstored in the code associated with the ad impression.
 57. The system ofclaim 54, wherein a bid is submitted for the ad impression by an adserver based upon prior activity associated with the stable identifierof the mobile device.
 58. The system of claim 57, wherein a bid issubmitted for the ad impression by an ad server upon: receiving a bidrequest for an ad impression in a native application installed on themobile device, where the bid request identifies the mobile device viaits stable identifier; and determining, by the ad server, that a mappingbetween the transient identifier and the stable identifier does notexist.
 59. The system of claim 57, wherein a bid is submitted for the adimpression by an ad server upon: receiving a bid request for an adimpression in a native application installed on the mobile device, wherethe bid request identifies the mobile device via its stable identifier;and determining, by the ad server, that a mapping between the transientidentifier and the stable identifier has expired.
 60. The system ofclaim 57, wherein a bid is submitted for the ad impression by an adserver upon: receiving a bid request for an ad impression in a nativeapplication installed on the mobile device, where the bid requestidentifies the mobile device via its stable identifier; and determining,by the ad server, that a mapping between the transient identifier andthe stable identifier has been invalidated by a change in networkconnectivity for the mobile device.
 61. The system of claim 1, whereingenerating a transient identifier for the mobile device and mapping thetransient identifier to a stable identifier of the mobile device isinitiated by a pixel called from a native application installed on themobile device.
 62. The system of claim 1, wherein executing the firstinstructions to retrieve the stable identifier of the mobile devicecomprises: identifying, by the browser application executing the firstinstructions, a locally-stored value that includes a first stableidentifier and extracting the first stable identifier from thelocally-stored value; calling, by the browser application executing thefirst instructions, the service endpoint, and passing the first stableidentifier as an argument; generating, by the service endpoint, atransient identifier; determining, by the service endpoint, a secondstable identifier of the mobile device using one or more of thetransient identifier, the first stable identifier, and a mapping betweenthe transient identifier and a third stable identifier; receiving, bythe browser application executing the first instructions, the secondstable identifier from the service endpoint; and storing, by the browserapplication executing the first instructions, the second stableidentifier in a locally-stored value.
 63. The system of claim 62,wherein the service endpoint updates a mapping between the transientidentifier and the third stable identifier using the received firststable identifier.
 64. The system of claim 62, wherein thelocally-stored value is in one or more of: a first-party cookie, athird-party cookie, a partitioned third-party cookie, a browser cache, apartitioned browser cache, or a local storage.
 65. The system of claim62, wherein when a locally-stored value that includes the first stableidentifier is not identified: the browser application, executing thefirst instructions, sets the first stable identifier to a null value.66. The system of claim 62, wherein when the second stable identifierreceived from the service endpoint is a null value: the browserapplication, executing the first instructions, clears the locally-storedvalue that includes the first stable identifier.
 67. The system of claim62, wherein when the second stable identifier received from the serviceendpoint is a non-null value and the locally-stored value that includesthe first stable identifier is not identified: the browser application,executing the first instructions, sets the locally-stored value thatincludes the second stable identifier.
 68. The system of claim 62,wherein when the second stable identifier received from the serviceendpoint is a non-null value that is different from the first stableidentifier: the browser application updates the locally-stored value toinclude the second stable identifier determined by the service endpoint.69. The system of claim 62, wherein the stable identifier included inthe locally-stored value is an encrypted value derived from the stableidentifier.
 70. The system of claim 69, wherein the service endpointgenerates the encrypted value using the second stable identifier, atimestamp, a random salt value, and a secret symmetric encryption key.71. The system of claim 9, wherein executing the third instructions toidentify the mobile device to an ad server or an RTB (real-time bidding)platform comprises: determining, by the browser application, alocally-stored value that includes the stable identifier; extracting, bythe browser application, the stable identifier from the locally-storedvalue; and passing, by the browser application, the stable identifier tothe ad server or the RTB platform.
 72. The system of claim 1, whereingenerating a transient identifier for the mobile device and mapping thetransient identifier to a stable identifier of the mobile device usingat least one call to a service endpoint coupled to the mobile devicecomprises: determining, by the mobile device, whether sharing of thestable identifier of the mobile device is disabled in the mobile device;and sending, by the mobile device, a null value for the stableidentifier of the mobile device when sharing of the stable identifier isdisabled in the mobile device.
 73. The system of claim 1, whereinretrieving the stable identifier of the mobile device using at least onecall to the service endpoint comprises determining whether the serviceendpoint has a non-expired second mapping between the stable identifierof the mobile device and a timestamp.
 74. The system of claim 73,wherein the second mapping between the stable identifier of the mobiledevice and a timestamp expires after a given time.
 75. The system ofclaim 73, wherein when the service endpoint does not have a non-expiredsecond mapping between the stable identifier of the mobile device and atimestamp, the service endpoint returns a null value for the stableidentifier of the mobile device to the browser application.
 76. Thesystem of claim 71, wherein the browser application passes a null valuefor the stable identifier of the mobile device to the ad server or theRTB platform.
 77. The system of claim 73, wherein the second mappingbetween the stable identifier of the mobile device and the timestampexpires after 24 hours, 48 hours, or 72 hours.
 78. The system of claim73, wherein a native application on the mobile device: generates one ormore bid requests associated with one or more ad impressions in thenative application, the one or more bid requests including the stableidentifier of the mobile device; wherein the one or more bid requestsare processed by an ad server or an RTB platform and sent to at leastone second remote computing device; wherein the at least one secondremote computing device extracts the stable identifier from the one ormore bid requests; and wherein the at least one second remote computingdevice updates the second mapping between the stable identifier of themobile device and the timestamp with the current time.
 79. The system ofclaim 78, wherein updating the second mapping between the stableidentifier of the mobile device and the timestamp comprises creating thesecond mapping between the stable identifier of the mobile device andthe timestamp if the second mapping does not exist, or changing thetimestamp to the current time if the second mapping exists.